Modelling nitrogen transport and transformation in a transplanted rice field experiment with reduced irrigation

Application of water-saving irrigation technologies in transplanted rice (TPR) cultivation resulted in different soil water regimes compared to traditional flood irrigation and consequent diverse nitrogen transport and losses in paddy fields. In this study, nitrogen transport and transformations in a TPR field under multiple shallow irrigation (MSI) conditions in the Taihu Lake Basin of Eastern China were observed and simulated (Hydrus-1D model) during the 2008 and 2009 seasons based on a previous study. MSI controlled well the depth of floodwater and reduced nitrogen losses substantially through percolation and surface runoff, in particular during the 2008 season with relative less rainfall. Nitrogen balance analysis showed that both denitrification and NH₃ volatilisation were the two major paths of nitrogen loss during the two seasons. Most nitrogen transformations occurred in top soil (0–40?cm) during early-middle seasons. The overall nitrification and denitrification differed slightly between the two seasons but largely between soil depths, averagely 92.7% and 73.0% of respective total in a 120?cm soil profile occurred in 0–40?cm soil, respectively. MSI method coupled with deep applied fertiliser is recommended to substantially reduce nitrogen losses through surface runoff, percolation, and NH₃ volatilisation in TPR fields.